1. Field of the Invention
This invention relates to an image displaying method and apparatus for displaying an image on an image displaying means, such as a CRT display device or a liquid crystal displaying device. This invention particularly relates to an image displaying method and apparatus, wherein a gradation converting process is carried out on an image signal and in accordance with a predetermined gradation converting table, and a visible image, which is represented by an image signal having been obtained from the gradation converting process, is displayed on an image displaying means.
2. Description of the Prior Art
Heretofore, in cases where an image is displayed on an image displaying means, such as a CRT display device or a liquid crystal displaying device, a gradation converting table for converting the gradation characteristics of the image displaying means (i.e., the relationship between the image signal value and the logarithmic value of the luminance on the image displaying means) into linear characteristics is prepared. A gradation converting process is then carried out on the image signal and in accordance with the gradation converting table. A visible image, which is represented by the image signal having been obtained from the gradation converting process, is displayed on the image displaying means.
However, it often occurs that the luminance of the image displaying means is depleted due to deterioration of the display surface of the image displaying means (for example, the fluorescent screen of a CRT display device), deterioration of an electron gun used for carrying out light emission display (or back light in a liquid crystal display device). FIG. 8A shows the luminance characteristics representing the relationship between the image signal and the luminance of the image displaying means. In FIG. 8A, Lorg represents the luminance characteristics before being depleted, and Ldep represents the luminance characteristics after being depleted. As illustrated in FIG. 8A, in cases where the luminance of the image displaying means is depleted, even if the same level of voltage is applied to the image displaying means, the same level of luminance as the original level of luminance cannot be obtained. As illustrated in FIG. 8B, if the luminance of the image displaying means is thus depleted, in cases where the gradation converting process is carried out on the image signal and in accordance with the gradation converting table, the gradation characteristics .gamma.org before being depleted cannot be obtained on the image displaying means, and the visible image will be reproduced with the gradation characteristics .gamma.dep after being depleted. With the gradation characteristics .gamma.dep after being depleted, the contrast of a high image density portion (i.e., a low luminance portion) A cannot be reproduced, and details of the portion A become imperceptible. If the portion of the low luminance (the high image density) in the image is not reproduced, the problems will occur in that the image information is lost, and the feeling of the image becomes different from the correct feeling.